Polyurethane foam metering apparatus

ABSTRACT

The polyurethane foam metering apparatus comprises a mixing chamber bored out in a core (3) of self-lubricating synthetic material, which core is gripped tightly in a hollow metallic cylinder detachably mounted on a support, in such a manner as to form a demountable cartridge, and compressed at right angles to feed orifices, so as to improve the seal of the valve rod (8) and to prevent infiltration of reactants into the mixing chamber when the latter is closed off by the valve rod (8).

BACKGROUND OF THE INVENTION

The present invention relates to a metering apparatus for polyurethanefoam arising from the reaction of two reactants fed separately viaseparate feed orifices into a mixing chamber formed from a bore providedaxially in a core of self-lubricating synthetic material, which core ismounted in a hollow metallic cylinder and provided over a first lengthfraction with an angular narrowing around which is fitted a metallicsleeve on which a tightening member acts, in such a manner as to subjecta second fraction of core of self-lubricating synthetic materialsurrounding the feed orifices to a compressive prestress at right anglesto these orifices, so as to improve the seal of the joint formed by thebore and a valve rod sliding inside the bore under the action of anactuator in order to actuate the flow of two reactants flowing throughthe feed orifices into the mixing chamber, and comprising a solventreceptacle disposed in the extension of the mixing chamber and traversedby the valve rod.

The reliability of a polyurethane foam metering apparatus depends mostlyon the perfection of the sealing joint between the valve rod and thefeed orifices of the mixing chamber. The slightest infiltration ofreactants between the Teflon® core and the valve rod, when the latter isin the closing-off position, causes the valve rod to jam and the feedorifices to be obstructed because of the tendency of the reactants toreact with each other instantaneously.

Thus, there is known from document U.S. Pat. No. 4,568,003, a meteringgun for polyurethane foam arising from the reaction of polyol and apolyisocyanate separately feeding a mixing chamber.

The mixing chamber is constructed by means of two half-shells made fromstainless steel which are capable of withstanding the mechanicalstresses exerted during the operation of the metering gun. The first andsecond half-shells are disposed in colinear alignment in order to forman internal longitudinal cavity. A core made from Teflon is insertedfrom one side of the cavity and is retained inside the cavity by meansof the walls of the second half-shell and by means of a retaining ring.

The mixing chamber has two feed orifices via which two fluid componentsare fed separately into the said mixing chamber. A valve rod slidesinside the bore in order to actuate the flow of the two reactantsflowing through the feed orifices towards the central bore of the coreand in order to guide the stream of foam spurting out of the mixingchamber.

It enables, in a first position, the reactants to flow through the saidfirst and second orifices and, in a second position, prevents the flowof the reactants through these orifices. The valve rod is actuatedforwards or backwards by means of a pneumatic, electric or hydraulicactuator detachably fixed to the valve rod by means of a laterallyfitting coupling part.

The core is maintained under a compressive prestress applied along anaxial and radial direction via the walls of the second half-shell andvia the retaining ring, this prestress being exerted by means of aseries of dish-shaped washers, called Belleville washers, maintained intheir appropriate position by means of a lip formed at the contact endof the two half-shells. The core is provided with an axial borelongitudinally traversing this bore and in communication with theoutside of the mixing chamber and with the reservoir formed on the otherside of the cavity defined by the first half-shell. Inside the reservoiris a cleaning fluid or solvent, such as a cellulosic solvent for thepolyurethane foam.

By virtue of the compressive prestress exerted on the Teflon® core, aperfect seal is long-lastingly ensured between the bore and the valverod. This seal prevents any infiltration of reactants into the mixingchamber but, however, it does not manage to prevent a gradual saturationof the solvent with reactants and with foam.

From document EP-A-0,068,670, there is known an apparatus for dispensinga mixture of liquid reactants fed separately via separate feed orificesinto a mixing chamber formed from a bore provided axially in acylindrical core of self-lubricating synthetic material. The core isprovided over a first length fraction with an annular narrowing aroundwhich is fitted a metallic sleeve on which a tightening member acts, insuch a manner as to subject a second fraction of core ofself-lubricating synthetic material surrounding the feed orifices to acompressive prestress at right angles to these orifices so as to improvethe seal of the joint between the bore and a valve rod sliding insidethe bore under the action of a actuator in order to actuate the flow oftwo reactants.

The tightening member is a clamp held in place by a pair of screws. Sucha clamp ensures the correct orientation of the core of syntheticmaterial in the extension of the hydraulic actuator only when the twoscrews are fully tightened. It has the drawback that a furthertightening of the clamp with a view to adjusting the compressiveprestress of the synthetic core is no longer possible.

From document U.S. Pat. No. 3,945,569, there is also known a meteringapparatus for polyurethane foam arising from the reaction of two liquidreactants fed separately via separate feed orifices into a mixingchamber bored out in a core of self-lubricating synthetic material,which core is tightly held in a cylindrical metallic cavity by means ofa cover non-detachably fixed to the abovementioned cavity by means ofplastic deformation. The core has a collar on which the cover acts andbears on a non-demountable cartridge disposed in its extension andcompressed at right angles to the feed orifices.

The mixing chamber forms a tamper-proof unit in which the compressiveprestress is imposed once and for all during the plastic deformation ofthe cover.

Further tightening of the cover with a view to adjusting the compressiveprestress is not possible.

There is known from document EP-A-0,204,577, a polyurethane foammetering apparatus comprising a mixing chamber and a metering rod whichare easily demountable. The mixing chamber is formed from a bore,axially provided in a core of self-lubricating synthetic material,having a tapered shoulder in which two diametrically opposed feedorifices are provided. The core is housed, by tightening, in a cavity ofthe metering apparatus of corresponding shape.

A valve rod slides inside the bore of the core in order to actuate theflow of two reactants towards the mixing chamber and in order to guidethe stream of foam spurting out of the latter.

The core of self-lubricating synthetic material is subjected to acompressive prestress perfectly aligned along its longitudinal axiswhatever the degree of tightening, by means of a cap provided with aninternal thread screwed over one end of the abovementioned cavity of themetering apparatus provided with a corresponding external thread. Thecore is maintained at right angles to the feed orifices under acompressive prestress perpendicular to the shoulder. Furthermore, thecore comprises a metallic aligning ring enabling the valve rod to beguided and any seizing to be avoided.

However, the free end of the core made from deformable syntheticmaterial emerges into the free air far from the tightening cap and doesnot manage to prevent the stream from spurting or suddenly deviating.

SUMMARY OF THE INVENTION

The present invention aims to overcome These drawbacks and sets out ametering apparatus comprising a tightening member which ensures thecoaxiality of the core of synthetic material whatever the degree oftightening of the tightening member.

It relates to a metering apparatus such as described in the firstparagraph of the present document, which metering apparatus ischaracterized in that the core (3) is provided over a first lengthfraction with an angular narrowing around which is fitted a metallicsleeve (15) on which the tightening member (13) acts, in such a manneras to subject a second fraction of core of self-lubricating syntheticmaterial surrounding the feed orifices (5, 6) to a compressive prestressat right angles to these orifices.

The cap, detachably fixed by screwing action at the front end of themetallic cylinder, enables the core of self-lubricating syntheticmaterial to be subjected to a compressive prestress perfectly alignedalong the longitudinal axis of the metallic cylinder, in such a manneras to ensure a perfect seal of the joint formed by the core ofself-lubricating synthetic material and the valve rod.

The compression of the Teflon® core at right angles to the feed orificescorresponds to a well-defined value when a series of Belleville washersis inserted between the core of self-lubricating synthetic material andthe metallic sleeve.

In one particular embodiment, the core of self-lubricating syntheticmaterial is provided, in the vicinity of an intermediate portion of themetallic cylinder, with an aligning ring whose bore is the extension ofthe bore of the core. The aligning ring and an O-ring type joint at therear end of the metallic cylinder constitute a double point of bearingand enables the valve rod to be guided along the Teflon® core withoutany seizing.

In order to assemble the first embodiment of the metering apparatus, theprocedure is as follows:

the valve rod is drawn right back;

the used-up solvent is discharged after the front end of the meteringapparatus has been tilted down;

the metering apparatus is rinsed out with a fresh solvent after thefront end has been brought back up;

the valve rod is pushed back into the core and

the latter is subjected to a compression obtained by tightening the capon the metallic cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

These particular features and details of the invention together withothers will become apparent from the detailed description includedherein of an embodiment of a metering apparatus according to theinvention, with reference to the attached drawings, given by way ofnon-limiting information, of the invention.

In these drawings:

FIG. 1 is a perspective view of a metering apparatus according to theinvention;

FIGS. 2 and 3 are sectional views of a metallic cylinder detached fromthe support shown in FIG. 1. They show, respectively, the closed-off andopen positions of the mixing chamber with the aid of the valve rod;

FIG. 4 is an exploded view of the metallic cylinder illustrated in FIG.2;

FIGS. 5 and 6 show the closed-off and open positions of the mixingchamber in a second embodiment of the metering gun according to theinvention.

In these figures, the same reference symbols designate identical and/orsimilar elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in FIG. 1, a polyurethane foam metering apparatusaccording to the invention, designated in its entirety by the referencesymbol 1, comprises a hollow cylinder 2 housing a core ofself-lubricating synthetic material 3 of the Teflon® type piercedthrough by an axial bore 4 forming a mixing chamber and by two radialfeed orifices 5, 6. The hollow cylinder 2 is detachably mounted on asupport or a handgrip 7. The bore 4 is traversed by a valve rod 8sliding along the bore, under the actuation of a pneumatic or electricactuator 9, between a first position in which reactants can flow throughthe said first and second radial feed orifices 5, 6 into the mixingchamber and a second position which closes off the said feed orificesand prevents the flow of the reactants towards the mixing chamber.

The pneumatic or electric actuator 9 is fixed to the handgrip 7 with theaid of a pin while the hollow cylinder is detachably mounted on thesupport in the extension of the actuator by means of a threaded rod 11and of a knob 12.

The feed orifices 5, 6 are provided with a pair of valves and withappropriate feed pipes 38, 39 enabling the reactants to be fedseparately into the mixing chamber. The chemical reactants forming thepolyurethane foam are contained in drums, not shown.

In order to ensure a sealed contact between the valve rod 8 and theTeflon® core 3, the core is subjected to a compressive prestress atright angles to the feed orifices 5, 6 by tightening a metallic sleevesurrounding an annular narrowing provided in the core 3, over a portionof its length. The tightening is carried out with the aid of a threadedcap 13 screwed onto the front end of the hollow metallic cylinder 2.

By precompressing the fraction of core surrounding the feed orifices 5,6, the sealing of the valve rod 8 is improved and infiltration ofreactants into the mixing chamber is prevented when the latter is closedoff by the valve rod 8. The precompression forces are distributed overthe Teflon® core 3 with the aid of a series of Belleville washers 34.

The Teflon® core 3 is provided, in the vicinity of the central portionof the hollow metallic cylinder 2, with an aligning ring 16 made fromstainless steel having a circular cross-section of approximately 5 mm indiameter and a thickness of approximately 2 mm, the bore of which islocated in the extension of the bore of the core 3 (FIG. 4).

The bore as the aligning ring 16 is machined with a 5/1000 mm tolerancewith respect to the diameter of the transverse cross-section of thevalve rod 8 and has a conical portion 14 promoting the insertion of thevalve rod 8 into the bore 4.

The metallic cylinder 2 is thus provided, at each end and in the middle,with axial holes which guide the axial displacement of the valve rod 8.Thus, the latter does not run the risk of bending or of being jammedunder the forces which are applied to it by means of the actuatingactuator 9. Thus, premature wear of the core 3 is avoided and thelifetime and reliability of the metering apparatus 1 is extended. Thecore 3 compressive prestress permits compensation for the wear which thebore 4 would undergo. The valve rod 8 is closed off at right angles tothe rear hole of an O-ring sealing joint 17 and of a retention flange 28machined with a precision of 1/100th mm .

In the withdrawn or open position of the valve rod 8, a position inwhich the polyurethane foam is dispensed, a portion of the rod which waspreviously inside the bore 4 in order to close off the nozzle of thefeed orifices, is inserted into a receptacle 18 containing solvent. Thesolvent dissolves the accumulations of polyurethane foam which, in theabsence of this cleaning operation, would run the risk of closing offthe openings. However, the solvent receptacle 18 becomes graduallyenriched in reactants and the solvent has to be renewed from time totime.

According to the invention, the solvent in the receptacle 18 of thefirst embodiment is renewed by proceeding in the following manner:

the valve rod 8 is drawn back;

the used-up solvent is discharged after the front end of the meteringapparatus has been tilted down;

the metering apparatus is rinsed out with a fresh solvent after thefront end has been brought back up;

the valve rod 8 is pushed back into the core 3; and

the latter is subjected to a compressive prestress obtained bytightening the cap 13 on the metallic cylinder 2.

It suffices to use a few drops of solvent in order to renew the latter,because of the small volume of the receptacle 18 containing the solvent.Preferably ethylene glycol or MESAMOL® from BAYER® is used.

The dismantling of the mixing chamber has the advantage of requiringonly the defective parts to be replaced and not all the parts. Thus,many quite expensive parts such as, for example, the hollow metalliccylinder 2, the metallic cap 13 and the valve rod 8 (now, the latter isa precision-machined part made from high-quality steel) may be recoveredand reused as they are. Only the worn-out or damaged Teflon® core 3 hasto be replaced.

The dismantling of the mixing chamber also enables any obstruction to beremoved from the feed orifices 5, 6 and anything causing the valve rod 8to jam. It thus enables the solvent to be renewed. This is, therefore, apreventive-maintenance measure intended to avoid excessive pollution ofthe solvent and therefore untimely blocking of the metering apparatus 1.

In a second embodiment of the invention, illustrated by FIGS. 5 and 6,the actuating means and the mixing chamber form an insparable compactwhole assembled together onto a gun handgrip 7.

The actuating and controlling device consists of an interrupter trigger19 which actuates the opening or the closing of an electro-hydraulicclosing-off valve 31 of a temperature-regulating circuit 20 comprising ahydraulic pump 21, a filter 23 and a means for heating the solvent 32.The hydraulic pump 21, provided on the delivery side with a pressurecontrol valve, directs the solvent, pressurized at 100 bar, into achamber 29 of a hydraulic actuator 22 which actuates the valve rod 8.

Simultaneously, pressurized air is drawn into each of the drums in orderto deliver the reactants into the mixing chamber through the feed pipes38, 39 and the feed orifices 5, 6.

In order to make it possible for a constant metering of the polyurethanefoam components with the aid of a metering apparatus, it has been knownto provide the feed pipes 38, 39 of the metering apparatus with athermostatic heating means intended to keep the temperature of thecomponents constant and, in particular, that of the polyol.

It is known that the viscosity of the polyol varies strongly withtemperature and that in the absence of heating, certain difficulties areencountered in suitably metering each of the components after eachextended interruption in the operation of the metering apparatus.

In a preferred development of the metering apparatus according to theinvention, there is provision for a means of heating, not only each ofthe feed pipes, but also the head of the metering apparatus.

In fact, existing metering apparatuses have the drawback of discharging,during each cold start, a precursor foam mixture in which the componentsare not present in the required proportions. In general, a shortage ofpolyol in relation to isocyanate is observed because of the higherviscosity of the polyol at ambient temperature. This high level of theviscosity slows down the flow of the polyol and is the cause of aninsufficient metering of the polyol in relation to the isocyanate whoseviscosity is less sensitive to temperature variations.

This results in the precursor foam mixture not expanding either in therequired proportions and therefore not supplying the expected volume ofpolyurethane-foam filling. Now, a variation in the volume of foamdischarged by the metering apparatus seriously affects the quality andthe accuracy of the operations of an automatic machine.

In order to overcome this drawback, there is provision for freeing atleast one orifice for access into the receptacle from the outside with aview to renewing or circulating the solvent.

In a preferred development of the metering apparatus according to theinvention, the latter is provided with a temperature-regulating circuit20 in which a heating fluid is maintain in forced recirculation in aclosed loop similar to a hydraulic circuit. The heating fluid is asolvent 30, preferably MESAMOLL® raised to a temperature of 30°to 70° C.in a heated filter. The solvent 30 is moved with the aid of a constantdischarge hydraulic pump 21 provided on the delivery side with apressure-control valve. The hydraulic circuit also comprises a filter23, a means 32 for heating the solvent, for example by means of anelectrical resistance element, and a two-position actuating valve 31, asillustrated in FIG. 15.

On pressing the trigger 19 of the metering gun, the two-positionelectro-hydraulic valve 31 closes off the temperature-regulating circuit20 and causes an increase in the pressure of the solvent 30 downstreamfrom the pump 21. The pressurizes solvent serves as hydraulic fluid inorder to actuate the actuator 22 against a spring 35 and draws back thevalve rod 8 from the bore 4 by opening the feed orifices 5 and 6, whichenables the polyurethane foam components to flow separately towards themixing chamber.

Excess solvent delivered by the pump is released by a pressure controlvalve and returned to the pump.

On disengagement of the trigger 19 of the metering gun, the two-positionvalve frees the thermostatic hydraulic circuit. The spring 35 pushesback the valve rod 8 into the bore 4 and interrupts the metering offoam. The hydraulic pump 21 ensures the forced recirculation of the hotsolvent in a closed loop of the thermostatic hydraulic circuit andmaintains at constant temperature the pipes feeding each of thecomponents.

Thus, the head of the metering device 1 is always maintained at constanttemperature whatever the position of the trigger 19. In the restposition of the trigger, that is to say in the absence of injection, thehead is heated by the solvent which circulates in thetemperature-regulating circuit. By contrast, in .the operationalposition, when the circulation of the solvent is interrupted, the headof the metering apparatus is maintained at the same temperature by thepassage of the components of the foam.

This hydraulic fluid is forced to flow through a filter 23 into a closedcirculation loop comprising two non-return valves.

The pressing, by compressive prestress, of the core 3 ofself-lubricating synthetic material is performed with the aid of ametallic sleeve 15 and a cap 13 which is screwed onto a nozzle of themetering gun 1.

The mixing chamber is accessible from the outside by simply unscrewingthe cap 13. This unscrewing removes the compressive prestress and itbecomes possible to drawback the sleeve 15. After withdrawing the sleeve15, it thus becomes possible to replace the defective Teflon® core 3with a loss of time and of productivity which is reduced to the minimum.

I claim:
 1. A metering apparatus for polyurethane foam arising from thereaction of two reactants comprising a mixing chamber formed by a boreaxially provided in a core of self-lubricating synthetic material, intowhich said two reactants are fed separately via separate feed orifices,a hollow metallic cylinder in which said core of self-lubricatingsynthetic material is mounted, a cap fixed to one end of said hollowmetallic cylinder which subjects said core of self-lubricating materialto a compressive prestress at right angles to the feed orifices,producing a seal of the joint formed by said bore and a valve rodslidingly engaged inside said bore and a solvent receptacle disposed insaid cylinder adjacent said mixing chamber and traversed by said valverod, the position of said valve rod within said bore being determined byan actuator, said position of said valve rod regulates the flow of thetwo reactants through said feed orifices into said mixing chamber, saidcore being provided over a first length fraction with an annularnarrowing around which is fitted a metallic sleeve, said cap includinginternal threads and screwed onto said hollow metallic cylinder, saidcylinder being provided with corresponding external threads so that saidcap acts upon said metallic sleeve in such a manner as to subject, bytightening the cap, a second fraction of said core of self-lubricatingsynthetic material surrounding said feed orifices to said compressionprestress at right angles to said feed orifices.
 2. A metering apparatusfor polyurethane foam as defined in claim 1, wherein at least oneBelleville washer is disposed between said metallic sleeve and a portionof said core of said synthetic material.
 3. A metering apparatus forpolyurethane foam as defined in claim 1 wherein said actuator is ahydraulic actuator disposed within said solvent receptacle.
 4. Ametering apparatus for polyurethane foam as defined in claim 3 whereinsaid metering apparatus is provided with a thermostatic heating meansproviding hydraulic fluid which is heated to a predetermined temperaturefor actuating said hydraulic actuator.
 5. A metering apparatus asdefined in claim 4 wherein said hydraulic fluid is a solvent.
 6. Ametering apparatus for polyurethane foam as defined in claim 5 whereinsaid metering apparatus is provided with a temperature regulatingcircuit which comprises an hydraulic pump having a constant dischargerate, a filter disposed on the delivery side of said hydraulic pump,said thermostatic means for heating the solvent and an electro-hydraulicvalve wherein said temperature regulating circuit is filled with saidsolvent and wherein said solvent hydraulically regulates the position ofthe hydraulic actuator connected to said valve rod in said mixingchamber.
 7. A metering apparatus for polyurethane foam as defined inclaim 1, wherein said cap and said core of self-lubricating syntheticmaterial are removable to provide access to said solvent receptacle. 8.A method for assembling a metering apparatus for polyurethane foamwherein the metering apparatus comprises a mixing chamber formed from abore axially provided in a core of self-lubricating synthetic materialdisposed within a hollow metallic cylinder, the mixing chamber includingtwo separate feed orifices for feeding two separate foam reactants intosaid mixing chambers, a solvent receptacle disposed coaxially adjacentto said mixing chamber and a valve rod slidingly engaging said solventreceptacle and wherein said core of synthetic material is subjected to acompressive prestress at right angles to the feed orifices, said methodincluding the following steps: said valve rod is drawn back; solventcontained in said solvent receptacle is discharged by tilting down afront end of said metering apparatus; said metering apparatus is rinsedout with fresh solvent after the front end of said metering apparatushas been brought back up, said valve rod is slidingly engaged back intosaid core, and said core of synthetic material is subjected to acompression obtained by tightening a cap which threadedly engages an endof said metallic cylinder thereby producing a compressive prestress upona metallic sleeve in place upon said core of synthetic material so as toproduce a seal between said bore and said valve rod sliding inside saidcore of said synthetic material.
 9. A polyurethane foam meteringapparatus comprising:a hollow, generally cylindrical metallic housingincluding a front end having an external threaded portion and an opposedrear end, including an inner core-receiving cavity extending inwardlyfrom the front end to an inner shoulder defined in said housingintermediate said front end and rear end and a solvent receptacleportion extending inwardly from said rear end to said inner shoulder; agenerally cylindrical core member of self-lubricating material includinga front end, a rear end and a central, longitudinally extending axialbore defining a mixing chamber, said core member having a stepped outerconfiguration including a rearward major diameter portion and a forwardminor diameter portion and defining a radial bearing surfacetherebetween, said core member being telescopically received in saidcore-receiving cavity so that its rearward major diameter portion abutssaid inner shoulder; a pair of reactant feed orifices extending throughsaid housing and said rearward major diameter portion of said coremember and into said mixing chamber; a valve rod received in saidhousing and including a front end portion extending into said rear endof said housing, through the solvent receptacle portion through saidinner shoulder and slidably received within the central axial bore ofsaid core member, the valve rod being movable between a forward closedposition wherein said valve rod extends forwardly into said mixingchamber of said core to block entry of reactants into said mixingchamber through said feed orifices and a retracted open position whereinsaid valve rod is withdrawn from said core member to a position rearwardof said feed orifices to thereby permit reactants to flow through saidorifices and into said mixing chamber; an elongated sleeve membertelescopically, and slidably received over said forward minor diameterportion of said core member within said core-receiving cavity; a capincluding an internal threaded portion adapted for threaded engagementwith the external threaded portion on the front end of said housing andarranged so that tightening of the cap urges the sleeve member againstthe radial bearing surface of said core member against said innershoulder of said housing, thereby providing a localized compressivepre-stress adjacent said feed orifices to provide a lasting effectiveseal between the core member and said valve rod; and means forreciprocally moving said valve rod between said open and closedpositions.
 10. A metering apparatus as defined in claim 9, wherein saidmeans for moving the valve rod comprises a hydraulic piston and cylinderactuator connected to a rearward end of said valve rod.
 11. A meteringapparatus as defined in claim 10, wherein said hydraulic piston andcylinder actuator is defined in said solvent receptacle portion of thehousing.
 12. A metering apparatus as defined in claim 11, wherein ahydraulic fluid used to move the hydraulic piston in the actuator is asolvent fluid for polyurethane foam and the reactants.
 13. A meteringapparatus as defined in claim 12, wherein said solvent fluid ismaintained at a predetermined elevated temperature to heat the meteringapparatus and thereby control polyurethane foam quality.